Acquired images may contain geometric distortions—such as radial, projective, and spherical distortions, and chromatic aberration—that can be difficult to correct. For example, it is desirable to correct a set of microscopy images acquired with one or more cameras (e.g., each capturing different spectral bands) for geometric distortions, or other optical aberrations or artifacts. Image correction is particularly important in applications such as the imaging of biological samples for clinical or research purposes, where acquired images must accurately represent the real object being imaged.
Where multiple images of a sample are obtained, either by a single camera or by multiple cameras, it is also desirable to register those images to create a composite image, and/or to relate the field captured in one image to the fields captured in the other images. For example, a set of images of a given biological sample may include images obtained at multiple spectral bands and/or at various magnifications. Such registration tasks may be complicated by the existence of geometric distortions in the individual images.
Where the set of images includes multiple fields of view (e.g., overlapping fields), registration of those multiple fields of view captured in the set of images may also be needed.
For an individual image, the relationship between coordinates of the image and coordinates in real space is not accurately known, without a frame of reference. Also, for a set of images of the same sample obtained using multiple cameras, the relationship between coordinates in an image and coordinates in real space may be different for different cameras, and, therefore, the images may be in bias with respect to each other. Furthermore, with more than a single field of view, the shift in the field of view in real space is not accurately known. Image registration, i.e., relating a set of images to a fixed coordinate system, may be needed for the set of images.
One technique that may be used to correct images for distortions is to use a test pattern having a known (or determinable) geometry in order to determine how to adjust images of a sample taken with the same camera under the same conditions, e.g., with the camera in the same fixed, relative position with respect to the subject being imaged as it was when imaging the test pattern. For example, a glass slide with fluorescently labeled beads of different sizes positioned thereupon can be used as a test pattern, and images of the bead test pattern can be used to determine how to adjust images of a sample taken under the same conditions. However, various difficulties may be encountered when using real beads as a test pattern for image adjustment. One of the difficulties is that different magnifications require different bead sizes. In addition, beads may not properly disperse, or they may be too difficult to image clearly. Moreover, the imaging and image correction procedure can be tedious and time consuming.
There is a need for a simpler, more effective method for adjusting one or more images of a sample to correct geometric distortions and/or to properly align the one or more images.